Guirguis S M, Yee J C, Stiffler D F
Biological Sciences Department, California State Polytechnic University, Pomona 91768, USA.
J Comp Physiol B. 1997 Jul;167(5):328-34. doi: 10.1007/s003600050081.
The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol.l-1, saturates above 0.3 mmol.l-1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and 0.6 mmol.l-1; net flux which is negative below 0.125 mmol.l-1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol.cm-2.h-1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 mumol.l-1. The benzothiazepine diltiazem was also effective at 50 mumol.l-1 while the dihydropyradine nifedipine was ineffective up to 100 mumol.l-1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 mumol.l-1; Ni2+ was also effective at 500 mumol.l-1 but Co2+ was ineffective up to 500 mumol.l-1. These results suggest that apical calcium channels in Xenopus laevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.
完整的、自由游动的非洲爪蟾的皮肤以一种与外部[Ca2+]成正比的方式向内转运Ca2+，直至约0.3 mmol·l-1，在高于0.3 mmol·l-1时达到饱和，且与电化学梯度相反。在外部浓度为0.016至0.6 mmol·l-1之间时，外流相对恒定；在低于0.125 mmol·l-1时为负的净通量在高于此外部[Ca2+]时变为正。异速生长分析表明，Ca2+内流和外流的比例约为表面积的2/3次方。夏季和秋季动物的内流没有显著差异；然而，秋季的外流更大，这导致从夏季的正平衡变为秋季的负平衡。离体皮肤显示支持近30 nmol·cm-2·h-1的Ca2+摄取率。顶端浴液中的苯基烷基胺维拉帕米在25 μmol·l-1时显著抑制了这一过程。苯并硫氮䓬地尔硫䓬在50 μmol·l-1时也有效，而二氢吡啶硝苯地平在高达100 μmol·l-1时无效。无机离子La3+在300 μmol·l-1时有效阻断Ca2+摄取；Ni2+在500 μmol·l-1时也有效，但Co2+在高达500 μmol·l-1时无效。这些结果表明，非洲爪蟾皮肤中的顶端钙通道具有与哺乳动物L通道和鱼类鳃Ca2+通道相似的特性。
